The nebula surrounding the open cluster NGC 6823 suffers an identity crisis. It’s not NGC 6820, as many sources claim, but rather a small knot of nebulosity 16 arcminutes in position angle 218 degrees (southwest by south) from the bright quadruple star at the cluster’s heart.
Here is NGC/IC Harold Corwin’s explanation:
NGC 6820 is a small knot of nebulosity, roughly 1′ × 1′, perhaps a reflection nebula around a few young stars or pre-stellar objects. It is specifically NOT the much larger HII region Sharpless 2-86 as has been many times been claimed, nor is it the cluster Collinder 404 = OCl 122, though that may
represent the stars involved with the nebula. Marth’s original observation with Lassell’s 48-inch reflector mentions only the nebulosity: “F, S, R, bM”. [Faint, small, round, brighter in the middle]
10-inch reflector, fairly bright with well defined edges, gray in color, oval shape with a center void. Both the NW and SW sides are brighter with greater concentration. The ring is much lighter, or thiner on the NW, and also on the SE, but more subtle. A 12th magnitude star lies, so very close to the east of the ring.
3.5-inch Maksutov-Cassegrain telescope at a magnification of 146x, the ring nebula is presented as very dim, round but mostly featureless. The central void can be seen, but fairly difficult.
102mm refractor at 175x, shows the ring as surprisingly bright on this night of exceptional viewing with sharp and well defined edges. The center void can be seen, but only as a lighter round gray spot, within the ring. Bright star just to the east.
Posted July 19, 2021 by rogerivester Categories:Uncategorized
Roger Ivester, North Carolina
&
Sue French, New York
July 2021
Report #150
NGC 6572, Planetary Nebula in Ophiuchus
Sharing Observations and Bringing Amateur Astronomers Together
This month’s target
Our object for the 150th monthly edition of the Observer’s Challenge is the tiny, but bright, planetary nebula NGC 6572, variously nicknamed the Emerald Nebula, the Blue Racquetball, and the Turquoise Orb. These names highlight the range of hues perceived by different observers. The nebula is young, perhaps only a few thousand years old. Its diminutive size led to its inclusion in some early star catalogs. NGC 6572 has a visual magnitude of 7.3, as determined by Stephen O’Meara, while its central star dimly shines at 13th magnitude. As with many planetary nebulae, published distances vary wildly. Values in the vicinity of 5000 light-years seem most likely. This pretty little gem was discovered in1825 by Wilhelm Struve.
NGC 6572 displays bipolar outflows in deep images. There’s evidence of interaction between the collimated outflows and the nebula’s elliptical shell. The interaction has broken up the elliptical shell such that parts of the shell have been accelerated, while the outflow has been slowed down and/or deflected. This supports the idea that such outflows are common in planetary nebulae and may play an important role in shaping nebular shells. https://ui.adsabs.harvard.edu/abs/1999ApJ…520..714M/abstract
Mario Motta: Observer from Massachusetts
NGC6572 is a very tiny object (16×12 arc seconds). Got this last week, poor night with some turbulence, with an H alpha, O3 , and S2 filters. Very short exposures as it is very bright. Visually a small “blue spot”.
Image attached, about 20 minutes each filter, O3 dominated…thus very blue. No detail that I can see. Only good image on line I found is by the Hubble, but can’t match that one! However, a nice object.
Complete Observer’s Challenge Report: Click on the following link…
I knew that fine detail of this planetary would not be possible from my back yard, using a 10-inch reflector. So, I chose to use a 6-inch f/6 reflector, mostly for convenience, but not really expecting much difference from the 10-inch.
With the 6-inch, this planetary is very small, mostly round and featureless, but with a pale bluish color.
This is definitely a large telescope object for the visual observer.
William Herschel discovered NGC 5746 on 24 February 1786 with his 18.7-inch reflector. His handwritten journal reads:” Extremely bright, much extended in the parallel, 8 or 9 arcminutes long, bright nucleus.”
A recent study by John Kormendy and Ralf Bender in the Astrophysical Journal presents NGC 5746 as a structural analog of our own galaxy. Both are “are giant, SBb–SBbc galaxies with two pseudobulges, i.e., a compact, disky, star-forming pseudobulge embedded in a vertically thick, ‘red and dead,’ boxy pseudobulge that really is a bar seen almost end-on.” According to the authors, the lives of these galaxies have been dominated by minor mergers and bar-driven evolution for most of the history of the universe. They place NGC 5746 at a distance of 26.7 Mpc (87 million light-years). https://ui.adsabs.harvard.edu/#abs/2019ApJ…872..106K/abstract
NGC 5746’s V(V_T) visual magnitude is 10.32 ± 0.13, and its surface brightness is 12.6. The galaxy’s visible extent through medium-size amateur telescopes under dark skies is in the vicinity of 7.4′ × 1.3′.
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Messier 3 (NGC 5272), Globular Cluster in Canes Venatici
Sharing Observations and Bringing Amateur Astronomers Together
Introductio
This month’s target
Charles Messier discovered M3 on 3 May 1764 with a 3.5-inch refractor. The French text of Messier’s catalog in the Connaissance des Temps translates into English as: “Nebula discovered between the Herdsman and one of the Hunting Dogs of Hevelius; it does not contain a star, the center is brilliant & its light imperceptibly fades, it is round; when the sky is good, one can see it with a refractor of one foot [at the time, telescopes were generally described by their length]; it is reported on the Chart of the Comet observed in 1779. Mémoires de l’Académie of the same year. Reexamined 29 March 1781, still very beautiful.”
According to William H. Harris’ Catalog Of Parameters For Milky Way Globular Clusters,
http://physwww.mcmaster.ca/~harris/mwgc.dat , M3 resides 10.2 kiloparsecs (~33,000 light-years) away from us and 12.0 kiloparsecs (~39,000 light-years) from the galactic center. It shines with an integrated V-magnitude of 6.19, and the spectral type of the integrated cluster light is F6. Does its color look slightly yellow to you?
“Sharing Observations and Bringing Amateur Astronomers Together“
This month’s target
William Herschel discovered this interacting galaxy pair on 15 February 1784 with his 18.7-inch speculum-metal reflector. His hand-written journal of the discovery reads: “Two nebulae almost close together. Perhaps 1½ or 2′ asunder, they are pretty considerable in size, and of a roundish form; but not cometic; they are very faint.” He also notes that on this night he first used: “A new, large object Speculum. It is very bright but not quite as distinct as my first, I shall however use it all the night.”
Together known as Arp 94, NGC 3226 and NGC 3227 are wedded in a gravitational dance 47.2 ± 0.2 million light-years away from us. Their complex dance has spawned a remarkable array of tidal tails as well as one tidal dwarf galaxy — a gravitationally bound condensation of gas and stars formed during the repeated encounters of the two parent galaxies.
Posted March 29, 2021 by rogerivester Categories:Roger's Articles
Jim Yeager has always allowed me to use any of his aerial photos, which over the years have included, a beautiful photo of the Barringer Crater in New Mexico, covered with snow, and the Mount Potosi Observing Complex in SW Nevada. Both of which I’ve used in previous blog articles and other.
I really like the following image, as I’ve never seen the Southern Cross.
Jim’s notes and photo:
Here is somewhat of clear picture taken with an iPhone using a 3 second exposure on a descent out of 41,000 feet about 100 miles north of Lima, Peru.
You can see Alpha and Beta Centauri pointing to the Southern Cross.
The residual cockpit lights, moonlight behind us, and the haze of high altitude cirrus kept us from seeing the Magellanic Clouds.
German astronomer Wilhelm Tempel discovered NGC 2685 in 1882 with an 11-inch refractor. Loosely translated, his discovery description reads: Good II-III; round; with a small star in the middle; stands 4′ south of a 10th-magnitude star.
In the Hubble Atlas of the Galaxies, Allan Sandage states, “NGC 2685 is perhaps the most unusual galaxy in the Shapley-Ames catalogue.” While most astronomers would agree with this, there remain various opinions as to why. NGC 2685 is generally regarded as a polar ring galaxy wrapped in exterior hoops of gas and dust aligned nearly perpendicular to the plane of the galaxy’s lenticular disk. The rings may have been birthed by a merger and/or accretion event. A less touted viewpoint is that this galaxy is strongly warped, and the semblance of rings is merely the result of projection effects.
This perplexing galaxy lies roughly 50 million light-years away from us. As seen photographically, the unusual array of gas, dust, and resultant stars entwining the Helix gives rise to its name. The galaxy may also house a supermassive black hole. Sue French
I was fortunate to meet Al Nagler a few years ago at the Southern Star Astronomy Convention in Little Switzerland, North Carolina.
Al gave a great presentation concerning eyepiece designs and calculations, based in-part on the above link.
The story:
There was a cancellation by a scheduled Southern Star participant, the last minute. I knew Sue French and Alan were at NEAF. So I called Sue via telephone, asking if Al Nagler was there, and if so would he be interested in giving a presentation for the convention.
Sue called back and said Al was “indeed” interested. I got things worked out with the Charlotte Amateurs and plane tickets for both Al and his wife…and the rest is history.
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